Will I get skinnier if I walk everyday in the morning?

I really enjoy walking. But now that it's summer and it's really hot, I start walking around 6:00 AM. I walk at least 1 to 2 miles if I do go for a walk. I just started walking because I am tired of staying at home. I don't want to continue walking if I continue to get skinnier. People already call me a skeleton... What do you think I can do to gain more "meat" on my bones? I never really exercised or maintained a healthy diet before.